1. Field of the Invention
The present invention relates to a method for condensing an ore slurry in an ore treatment process of preparing an ore slurry from crude ores of nickel oxide ores that have been mined, and more specifically concerns a method in which in a condensing step of the ore slurry, by using a combination of a method for specifying the molecular weight of a flocculant and the dilution ratio upon addition thereof, a method for specifying the added amount of the flocculant and a method for specifying the ore slurry temperature after concentration, the concentration and viscosity of the ore slurry are adjusted so that it becomes possible to prevent the slurry from causing a failure to be transported to a leaching process that is the post process.
2. Description of the Related Art
In recent years, a high temperature and pressure acid leach method (sometimes referred to as “HPAL method”) using sulfuric acid, which is one of wet-smelting methods, has been utilized, as a smelting method in which, from nickel oxide ores containing nickel and cobalt respectively in a range from about 1.0 to 2.0% and in a range from about 0.1 to 0.5%, relative to the entire amount, as crude ores, nickel and cobalt are recovered.
This HPAL method is a smelting method including a leaching process in which, for example, sulfuric acid is added to an ore slurry of nickel oxide ore so that the slurry is leached under a high temperature and a high pressure to obtain a leachate containing nickel and cobalt; a neutralizing process in which the pH of the leachate containing impurity elements together with nickel and cobalt is adjusted so as to form a neutralized precipitate slurry containing impurity elements, such as iron, and a nickel recovering base solution that has been purified; and a sulfiding process in which a hydrogen sulfide gas is supplied to the nickel recovering base solution so that a nickel-cobalt mixed sulfide and a barren solution are formed (for example, see Japanese Patent Application Laid-Open No. 2005-350766).
In this method, generally, 90% or more of nickel and cobalt in the ore slurry are leached in the leaching process. Next, after the leachate has been separated, impurities in the leachate are separated and removed therefrom by a neutralizing method. Moreover, the nickel grade in the nickel-cobalt mixed sulfide thus obtained is 55 to 60%, and the cobalt grade therein is about 3 to 6% so that this is used as an intermediate material in the nickel-cobalt smelting process.
Here, the ore slurry of nickel oxide ores to be used is normally subjected to an ore treatment process for preparing a charging material into a smelting step from the crude ores after having been mined.
In this ore treatment process of the nickel oxide ores, for example, low-grade nickel oxide ores having a nickel grade of about 1.0 to 2.0% is formed into a slurry having a predetermined particle size and a concentration by classifying (sieving) and pulverizing steps including a multiple steps, and recovered and transferred to the leaching process as the post process.
More specifically, the ore treatment process is mainly classified into pulverizing and classifying steps and an ore slurry condensing step. In the pulverizing and classifying steps, crude ores are pulverized in a wet-type facility so that oversized particles and mixed matters are removed therefrom (for example, see Japanese Patent Application Laid-Open No. 2009-173967).
Since the ore slurry thus produced contains excessive moisture, the excessive moisture contained therein is removed in the next ore slurry condensing step (for example, see Japanese Patent Application Laid-Open No. H11-124640).
Since ore components contained in the ore slurry per same transporting amount are increased by this moisture removal, this process has an additional effect for improving the operating efficiency of the entire plant.
However, only condensing the ore slurry sometimes tends to make the viscosity of the ore slurry too high, and in such a case, the transporting capability of a pump for use in transporting the ore slurry from the ore treatment process to leaching process is exceeded. For this reason, a transporting failure occurs to cause a temporarily stoppage of the plant, and a subsequent reduction in the operating efficiency.
For this reason, in the operations of the conventional plant, the solid component concentration can be raised only within a range capable of carrying out the slurry transportation, and the resulting problem is that a high slurry solid component concentration and such a low-level yield stress as to easily allow the slurry transportation are not simultaneously satisfied.
The present invention has been devised to solve these problems, and its object is to provide a method of producing an ore slurry that has such a low-level yield stress as to easily allow a slurry transportation even when the slurry has a high concentration, so that no problems are raised in the transportation.